Implement authorization framework

[stephanarts]

At the moment there is no authorization framework implemented. This ticket is ment to keep track of all development on this subject.

[stephanarts]

Basic login mechanism is implemented in b85753d, still requires actual user management and some proper authorization matrix though.

[stephanarts]

At the moment there is code-duplication in the two login-paths. This already resulted in a security-issue when only one actually performed a login and the other one allowed everything where username==password. - This must be fixed.